The present invention relates to electrodeionization (EDI) and more particularly, a method for treating fluids via electrodeionization.
Electrodeionization (EDI), also known as electrochemical ion-exchange, is an advanced ion-exchange technology that combines the advantages of ion-exchange and electrodialysis. In electrodeionization processes, ion-exchange resins are sequestered in dilute feed compartments to increase the ionic conductivity, so that even with a very dilute ionic feed (10xe2x88x921 N), a stable operation with higher flux and lower energy consumption than electrodialysis, becomes possible. The electric power also splits the water molecule (H2O) in to H+ and OHxe2x88x92 ions and the resins are thus regenerated while the ions are removed.
EDI technology presently is used to make deionized water for boiler feed and high purity industrial water applications. There are also many other potential uses of such technology for organic process streams in a variety of industries. One problem encountered in the production of organics such as organic acids and amines is pH control. For example, efficient biocatalytic production of acids and amines is often limited to a narrow pH range for optimal productivity. The present invention provides very accurate pH control using EDI technology, which in combination with previous work at Argonne National Laboratory (ANL) relating to EDI cell design, results in superior production, separation and concentration of a wide variety of organics.
Ion exchange beads that are commonly used for EDI applications may contain strongly acidic resins containing for instance sulfonic acid groups, or strongly basic resins containing for instance quaternary ammonium groups. Other resins such as those with weakly acidic resins for instance carboxylic acid groups or weakly basic resins for instance amines groups are also used when required, and according to the invention may be mixed as required. These resin beads are cross-linked with polymers usually styrene divinyl benzene or acrylates. The resins can be gel type or macro-reticular type. Usually equivalent mixtures of cationic and anionic resins have been used in the EDI compartments. For specialized applications one type of resin or adsorbent beads mixed with ion-exchange resins may be used. A device useful in the practice of the present invention is disclosed in PCT Application WO 01/12292, the entire disclosure of which is incorporated by reference. Another publication disclosing resins applicable to EDI processes is the Terada et al. U.S. Pat. No. 6,071,397 issued Jun. 6, 2000, the entire disclosure of which is also incorporated by reference.
It is an object of the present invention to provide a method of controlling the pH or capturing ionic organics in an EDI process.
Another object of the present invention is to provide a method of transferring ionizable organics while controlling the pH in an EDI process and device.
Yet another object of the invention is to provide an economical method for continually producing organic acids and/or amines while controlling the pH to within one pH unit.
Briefly, the invention utilizes the previously mentioned ANL developments including ion-exchange resins having cation-exchange moieties and anion-exchange moieties immobilized relative to each other conferring ion-conductivity and liquid permeability to the material in an EDI stack continuously to produce, separate and concentrate dilute organics while controlling the pH thereof.
The invention also provides a method of controlling the pH of a fluid during electrodionization by adjusting one or more of the resin content in the wafers, adjusting the ratio of strong or weak acid resins to strong or weak base resins in the wafers, the concentration and amount of ionizable organic material flowing through the EDI stack and the current applied to the EDI stack while regenerating the resin, in situ.
The invention consists of certain novel features and a combination of parts hereinafter fully described, illustrated in the accompanying drawings, and particularly pointed out in the appended claims, it being understood that various changes in the details may be made without departing from the spirit, or sacrificing any of the advantages of the present invention.